DataFixing is a very complex subject and we do not take any responsibility for damaged worlds and or saves. If you are trying something out, please backup your worlds.

The name honestly explains what it does, it fixes data by converting an old data format to a newer one. DataFixers are used in cases ranging from renaming an item to The Flattening inside Minecraft.

Hold on a second you are probably going to need a lot of context first or you will be entirely confused, so just read on a bit more.

DataFixerUpper (DFU) is the library Mojang created for DataFixing. Without getting into 10 academic articles it uses Profunctor Optics and some other mathematical magic to transform the datasets.

DFU within Minecraft has been used to do many things including:

• The Flattening.
• Changing entity NBT so UUIDs are stored as Greatest and Least Significant bits instead of a String.
• Converting villagers to new 1.14 data format.
• Renaming Biomes.
• Renaming Entities.
• Renaming Items (both on ground, in entities and in BlockEntities)
• Changing block names.
• Anything else if you are willing to try to wrap your head around DSL (covered later on).

Next up is learning about Schemas… [Schemas Page is WIP and will come out soon]